Panel shaped heating surface for combustion chambers



A. BRUNNER Nov. 18, 1969 PANEL SHAPED HEATING SURFACE FOR COMBUSTION CHAMBERS Filed Dec.

Inventor A 4 FFPED BRU/V/VER United States Patent Office 3,478,724 Patented Nov. 18, 1969 3,478,724 PANEL SHAPED HEATING SURFACE FOR COMBUSTION CHAMBERS Alfred Brunner, Winterthur, Switzerland, assignor to Sulzer Brothers, Ltd., Winterthur, Switzerland, a I corporation of Switzerland Filed Dec. 26, 1967, Ser. No. 693,580 Claims priority, application Switzerland, Dec. 29, 1966, 18,767/ 66 Int. Cl. F22b 21/24 US. Cl. 122-235 Claims ABSTRACT OF THE DISCLOSURE The outermost tube of the panel is connected with either or both of an auxiliary feed tube or discharge tube of the same diameter upstream or downstream of the section exposed to the severest fire radiation. The auxiliary tubes connect with the headers to augment the flow of working medium through this tube section so as to effect the cooling of the tube section and to reduce the wall temperature of the tube section.

This invention relates to panel shaped heating surfaces for combustion chambers. More particularly, this invention relates to panel shaped heating surfaces composed of a plurality of tubes connected in parallel relation.

Generally, panel shaped heating surfaces for combustion chambers of a steam-raising plant are composed of a plurality of working medium conveying tubes connected in parallel between an inlet header and a discharge header. The tubes are usually twisted in the plane of the panel to convey the working medium in tortuous paths above the combustion chamber. The outermost tube of such panels usually contains the section of the panel which is exposed to the severest fire radiation and thus is endangered by an excessive temperature.

In order to combat the danger of exposure to an excessive temperature occurring in the exposed tube section, various means have been prepared. In one instance, a heating surface in the form of a connecting tube has been disposed upstream of the panel shaped heating surface. For example, the connecting tube has been disposed between the boiler drum and a superheater disposed in the flue. However, this arrangement has been disadvantageous since the panel shaped heating surface and the connecting tube do not form a unified structure which can be produced in a workshop and subsequently positioned in the combustion chamber and connected in place with the connection positions in an easy manner. In another instance, the outermost tube of the panel shaped heating surface has been made shorter or of a larger diameter than the other parallel connected tubes in the panel in order to convey a greater flow of working medium due to the smaller flow resistance. However, where the tube has been made shorter, the tube has not always been able to allow an adequate amount of working medium to flow therethrough. Also, where the tube has been made of larger diameter, the tube has absorbed more heat together with the larger flow of working medium. Further, the wall thickness of such an enlarged diameter tube has been greater than that of the other tubes in the panel such that the maximum tube wall temperature of the tube section most exposed to the severest fire radiation has not been sufficiently low. Finally, due to the larger diameter, the connecting bore in the inlet header and discharge header as well as the wall thickness of these headers must be increased.

Accordingly, it is an object of the invention to efficiently cool the tube of a panel shaped heating surface most exposed to the severest fire radiation.

It is another object of the invention to increase the flow of working medium through an outermost tube of a panel shaped heating surface without changing the diameter of the tube.

It is another object of the invention to provide a panel shaped heating surface which has a means to cool the tube most exposed to the severest fire radiation and is of unit construction.

It is another object of the invention to provide a panel shaped heating surface which is easy to construct and mount in place.

Briefly, the panel shaped heating surface of the invention is composed of tubes connected in parallel wherein the section of at least the outermost tube exposed to the severest fire radiation is connected by an auxiliary feed tube to the inlet header and an auxiliary discharge tube to the outlet header. This section is thus provided with a larger amount of working medium than the remaining parallel connected tubes of the panel through the auxiliary feed and discharge tubes.

The larger flow of working medium passing through the tube section exposed to the severest fire radiation is heated to a lesser extent than the flow in the other tubes so that the wall temperature of the tube section is lower. This ensures an adequate cooling of the tube section at all times. In addition, due to the greater velocity of fiow, a higher thermal transfer coeflicient between the wall of the tube section and the working medium is brought about so as to further reduce the temperature of the tube section.

The panel shaped heating surface of the invention can be manufactured, transported and installed as a unit while all the connecting bores of the inlet and outlet headers are of the same size.

In one embodiment, the connecting position of the auxiliary feed tube and of the auxiliary discharge tube is disposed on the outermost tube in the radiation shadow of that tube section exposed to the severest fire radiation.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a diagrammatic vertical sectional view through a combustion chamber of a steam raising plant incorporating a panel shaped heating surface of the invention;

FIG. 2 illustrates a view taken on line A B of FIG. 1; and

FIG. 3 illustrates a fragmentary view of a modified connection between a pair of auxiliary feed tubes and the outermost tube of a heating surface of the invention.

Referring to FIGS. 1 and 2, the combustion chamber 1 of a steam raising plant has walls covered with tubes 2. A plurality of panel shaped heating surfaces 3 extend vertically and in the flow direction of the flue gas flowing between the surfaces 3 at a mutual spacing of about 0.5 meter above the combustion chamber 1. Each heating surface 3 comprises a plurality of tubes 6b, 6c, 6d, 6e, 6i, 6g and 6h connected in parallel with respect to a working medium between an inlet header 4 and an outlet header 5. The tubes 6e to 6h are twisted in a meander shape in the plane of the panel while the outer tubes 6b to 6d are twisted in U-shape in the plane of the panel and, thus, have a shorter tube length than the inner tubes 62 to 6h. A firing system 7 is provided in the combustion chamber 1 below the heating surface 3.

The section 6b between positions C and D of the outermost tube 6b is exposed to the severest fire radiation from the firing system 7 during operation of the plant. In order to protect this section 6b, an auxiliary feed tube 6a and an auxiliary discharge tube 6a" are connected to the section 6b at the respective points C and D. The feed 3 tube 611' extends upwardly to the inlet header 4 to convey an auxiliary flow of working medium into the section 6b whereas the discharge tube 6a" extends upwardly to the discharge header 5 to convey an auxiliary fiow of working medium away from the section 6b.

In operation, with the firing system 7 fired up, the working medium in the inlet header 4 is distributed to the various tubes 6a to 6h and conveyed therethrough to the outlet header 5. The working medium passing through the auxiliary feed tube 611 is fed into the section 6b at point C to augment the flow in the tube 6b. This causes a larger amount of working medium to flow through the section 6b than through the other tubes 6c to 6h so that the section 6b is cooled at a greater rate to a greater degree while the highest tube wall temperature of the section 6b is maintained at a sufficiently low value.

Alternatively, the section 6b can be provided with either an auxiliary feed tube or an auxiliary discharge tube in order to increase the velocity and quantity of working medium flow through the section 6b.

Referring to FIG. 3, a plurality of feed tubes 6a can be connected into the tube section 6b exposed to the severest fire radiation. In this case, the auxiliary feed tubes 6a are disposed within the panel in the plane of the panel between the U-shaped outermost tube 6b and the next inner U-shaped tube 6e. Similarly, a pair of auxiliary discharge tubes (not shown) can be connected in a corresponding manner to the opposite end of the tube section 6b either in conjunction with or instead of the auxiliary feed tubes.

What is claimed is:

1. A panel shaped heating surface for a combustion chamber of a steam raising plant having an inlet header and an outlet header comprising a plurality of tubes for conveying a working medium therethrough between the inlet header and the outlet header, said tubes being disposed in the plane of the panel in parallel relation to each other with respect to the flow of working medium passing therethrough and at least one auxiliary tube con nected to a section of the outermost of said tubes at a first point to convey an auxiliary flow of working medium therethrough to augment the flow of working medium in said section of said outermost tube, said auxiliary tube being of the same diameter as said outermost tube.

2. A panel shaped heating surface as set forth in claim 1 wherein said auxiliary tube is a feed tube connected upstream of said section for feeding the auxiliary flow of working medium into said section.

3. A panel shaped heating surface as set forth in claim 2 which further comprises at least one auxiliary discharge tube connected to said section at a point downstream of said auxiliary feed tube for conveying the auxiliary flow of working medium out of said section.

4. A panel shaped heating surface as set forth in claim 1 wherein said auxiliary tube is a discharge tube connected downstream of said section for conveying the auxiliary flow of working medium out of said section.

5. A panel shaped heating surface as set forth in claim 1 wherein said outermost tube is shorter in length than the innermost of said tubes.

6. A panel shaped heating surface as set forth in claim 1 wherein said auxiliary tube is connected with said outermost tube in the radiation shadow of said section.

7. In combination with a steam raising plant having a combustion chamber, an inlet header for feeding a working medium into said chamber, an outlet header for conveying the working medium out of said chamber and a firing system in said chamber; at least one panel shaped heating surface for conveying the working medium from said inlet header to said outlet header above said firing system, said heating surface comprising a plurality of tubes connected in parallel to said inlet header and said outlet header, one of said tubes having a section exposed to the severest fire radiation of said firing system, and at least one auxiliary tube connected to one of said headers and said section for conveying an auxiliary flow of working medium therethrough to augment the flow of working medium through said section to cool said section.

8. The combination as set forth in claim 7 wherein said auxiliary tube is of the same diameter as each of said plurality of tubes.

9. The combination as set forth in claim 7 wherein said auxiliary tube is a feed tube connected to said inlet header and said section.

10. The combination as set forth in claim 9 which further comprises at least one auxiliary discharge tube connected to said discharge header and said section downstream of said feed tube for conveying the auxiliary flow of working medium out of said section.

References Cited UNITED STATES PATENTS 2,423,997 7/1947 Ruegg 126-109 1,842,235 1/ 1932 Barnes 122235 2,821,175 1/1958 Seidl 122-48l 3,060,908 10/ 1962 Brister et al. l22235 KENNETH W. SPRAGUE, Primary Examiner 

